With the development of electronic technology and the enhancement of environmental protection requirements, efficiency and stability become important factors for voltage converters design.
In high security requirements of adapter and charger applications, an isolation voltage converter including a primary circuit and a secondary circuit may be adopted, wherein a transformer of the isolation voltage converter is used to isolate the primary circuit and the secondary circuit. In a prior art secondary side regulated isolation voltage converter, a secondary side voltage or current signal is sampled for feedback regulations. A primary switch is switched on and off based on the sampled secondary side voltage or current signal so as to realize a constant voltage or constant current control. The prior art secondary side regulated isolation voltage converter can provide precise control of voltage or current. However, the prior art secondary side regulated isolation voltage converter may require a large number of components resulting in high power consumption and low efficiency. Moreover, an expensive optical coupler may be needed during sampling the secondary side current or voltage signal. Thus, the prior art secondary regulated isolation voltage converters may result in high cost and complex structure.
Currently, in order to reduce the number of components used and to remove the optical coupler, design of isolation voltage converters sensing primary side current or voltage for feedback regulations become a challenge.